I am not sure that they did assume the debt. I just assume that they did to acquire the property, that was otherwise worthless. If they hadn't, the banks and other creditor's would surely have liquidated the assets for whatever they were worth, if anything, and then we would have been left with nothing. Even the real estate probably owed a fortune in back taxes...Two problems with that.
1) The taxpayers should not should have not have assumed the debt. The railroads were bankrupt. The lenders presumbly knew (or should have known) about the shaky finances, and have been prepared to take the risk that they'd lose their money. I have no sympathy for the banks. I guess this is what is called "socializing 'private' debt," and it's a curse of our political and economic system.